The popularity of metal and metal oxide coated glasses in architectural and automotive design is well known. As reported prolifically in patent and other literature, such glasses, through the manipulation of the coating's layering system, usually by choice of metals and/or metal oxides and/or thicknesses, can usually achieve, quite acceptably, the degree of reflectance, transmittance, emissivity and durability, as well as the color desired. See, for example, in this respect, U.S. Pat. Nos. 3,935,351; 4,413,877; 4,462,883; 3,826,728; 3,681,042; 3,798,146; and 4,594,137 just to name a few.
It has also been well reported that while several reasonably acceptable techniques exist for applying such coatings, one of the most efficacious, and thus preferred, is the well known technique referred to as "magnetically enhanced sputter-coating". Such a technique is reported in U.S. Pat. No. 4,166,018, a recognized fundamental teaching on the subject. (See also, Munz et al. "Performance and Sputtering Criteria of Modern Architectural Glass Coatings" SPIE Vol. 325 Optical Thin Films, 1982 pp. 65-73.)
While efficacious for many known layer systems, the use of sputter-coating has been known to result in mechanical durability qualities less than that achieved by another known method called the "pyrolytic" technique. As a reverse function, however, sputter-coated systems often achieve better infrared reflectance than typical pyrolytic coatings. Also, sputter-coated glasses have generally been recognized as having superior optical and thermal performance characteristics than pyrolytically formed coatings, such as having improved coating uniformity, good emittance, and better solar performance characteristics. It is clear, that if a sputter-coating technique could be devised for a particular coating system wherein the mechanical durability qualities of the sputter-coated system could approach or equal that of a pyrolytic technique, while at the same time achieving the enhanced benefits of sputter-coated technology, a significant step forward in the art would be made. The subject invention described below, in the preferred embodiments thereof, achieves this long-felt need in the art.
In recent years, the popularity of coated glasses has occasioned numerous attempts at achieving a coated glass article which prior to heat treatment can be coated, and which thereafter, can be heat treated without adversely changing the characteristics of the coated glass article. One of the reasons for this is, for example, that it can be extremely difficult to achieve a uniform coating on an already bent piece of glass. It is well known that if a flat glass surface can be coated and thereafter bent, much simpler techniques can be used to get a uniform coating than if the glass has been previously bent.
Certain techniques have been developed in the past for making heat treatable glass articles which may then, and thereafter, be heat treated by way of tempering, bending, or a technique known as "heat strengthening". Generally speaking, many of these prior techniques have suffered from not being truly heat treatable at the higher elevated temperatures necessary to achieve economic bending, tempering, and/or heat strengthening (i.e. 1150.degree. F.-1450.degree. F.). In short, such techniques have often suffered from a need to keep the temperature at approximately 1100.degree.0 F. or less in order to achieve heat treatability without adversely affecting the glass or its substrate.
In this respect, however, two of the inventors of this invention have previously invented and offered for sale certain prior art coating systems which can be heat treated successfully at the higher, more elevated temperatures aforesaid, to achieve tempering, bending, or heat strengthening. Generally speaking, these prior art coating compositions find their uniqueness in a layering system which employs as a metallic layer, a high nickel content alloy which, in its preferred form, is an alloy known as Haynes 214, consisting essentially of 75.45% Ni, 4.00% Fe, 16.00% Cr, 0.04% C, 4.50% Al, and 0.01% Y (percentages are by weight). By using a high nickel content alloy, such as Haynes 214, and overcoating it with stoichiometric tin oxide (Sn O.sub.2) either alone or with other layers (such as an undercoating of the same stoichiometric tin oxide and/or an intermediate layer of aluminum between the top Sn O.sub.2 layer and the high content nickel alloy), it was found that heat treatability of glass articles at elevated temperatures of from approximately 1150.degree. F.-1450.degree. F. from about 2- 30 minutes, could be achieved without substantial degradation of color, durability, chemical resistance, emissivity, reflectance or transmittance. These compositions therefore constituted a significant improvement over prior heat treatable systems such as those disclosed in the following patents: U.S. Pat. Nos. 4,790,922; 4,816,034; 4,826,525; 4,715,879; and 4,857,094.
In addition to the above disclosures in the aforesaid patents, the Leybold "Spectrum" windshield glass system TCC-2000 is also known. In this system, four or five layers of metals and metal oxides are employed to obtain a sputter-coated glass which, being somewhat heat treatable at temperatures up to 1100.degree. F. may be used as a pre-coated glass for making bent or unbent, glass windshields, provided that rapid time limits are placed on the heat treatment. The layering from glass substrate outwardly usually includes a first layer of tin oxide, a second layer of nickel/chrome alloy (usually about 80/20), a third layer of silver, a fourth layer of the nickel/chrome alloy, and a fifth layer of tin oxide. In addition to the rather low upper limit on heat treatment temperatures and times, the resultant coatings are rather soft and exhibit such unacceptably low chemical resistance characteristics that they can realistically be used only on the inner surfaces of laminated glass windshields.
In the aforesaid U.S. Pat. No. 4,715,879 it is specifically taught that the layering system therein can not be achieved unless the protective layer of a metal oxide (e.g. tin oxide) be formed such that the oxide has an oxygen deficit (i.e. is non-stoichiometric). This, of course, requires delicate balancing in the manufacturing process. Heat treatability, in this respect, is also disclosed in U.S. Pat. No. 4,826,525. However, in this patent it is specifically taught that a layer of aluminum must be applied to achieve heat treatability.
The alloy most preferred for use as the high content nickel alloy (i.e. a nickel alloy having a nickel content greater than about 50% by weight) in the practice of this invention is an alloy produced by Haynes International Corporation known as Haynes Alloy No. 214. This alloy is a nickel-based, high temperature alloy that is known for its excellent resistance to oxidation, carburization, and chlorination. Its nominal chemical composition is as stated aforesaid. While this particular unique alloy, as well as nickel and/or other alloys thereof having a nickel content by weight of greater than about 50% have been found to be useful in the practice of the subject invention, it is not by the use of these alloys alone that the improvements achieved by the subject invention are realized. The improvements, instead, are realized from a unique layering system, as opposed to a particular layer in and of itself.
There are three different types of heat treatments that are generally employed in working glass for architectural or automotive purposes; namely, bending, tempering, and a lesser form of tempering called "heat strengthening" or "hardening". When bending without tempering conventional 1/4" clear float glass, for example, times of 10-30 minutes at 1150.degree. F. or more, are generally necessary to use. In heat strengthening or tempering such glasses, with or without bending, temperatures as high as about 1450.degree. F. (e.g. 1150.degree. F.-1450.degree. F.) are normally employed for about 2-5 minutes. As can be seen, there are significant drawbacks to many of the known or reported prior art techniques which are limited in their upper temperatures, for providing heat treatable, coated glasses, particularly of the efficacious sputter-coated type. By the term "heat treatable" as used herein, therefore, is meant that the coated (layered) glass can undergo one or more of the above three treatments, and that in the preferred forms of this invention heat treatability can take place for the requisite periods of time at temperatures of from 1150.degree. F.-1450.degree. F.
Coated glasses for use in architectural or automotive design (e.g. vehicular privacy windows) generally have eight (8) characteristics which determine their efficacy and/or marketability: commercial feasibility, durability (mechanical resistance to abrasion), chemical resistance, long-term stability, emissivity, transmittance, reflectivity, and color. In prior systems, including those developed by two of the inventors herein, as reported hereinabove, some of the characteristics had to be significantly compromised in order to achieve the necessary degree of acceptability for the remaining characteristics. For example, in the case of the inventors' prior systems, while high temperature heat treatability was achieved, mechanical durability was not optimized. For this and other reasons, therefore, it is apparent that there exists a need in the art for a heat treatable, coated glass useful in architectural and/or automotive design which does not significantly compromise any of the above eight characteristics, and which preferably also may be heat treated (i.e. bent, tempered and/or heat strengthened) at the upper temperature ranges and times of such treatments. There is also a need for a coating which can be formed by sputter-coating techniques, but which also achieves the mechanical durability of pyrolytically formed coatings.
It is a purpose of this invention to fulfill the above-described needs, as well as other needs apparent to the skilled artisan from the following detailed description of this invention.